Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners.
In a bowl, whisk together flour, baking powder, cream of tartar, baking soda, and salt. Set aside.
In another bowl, whisk melted butter with 1 cup of sugar until well combined. Add the egg, Greek yogurt, milk, and vanilla extract, mixing until smooth.
Gradually add the dry ingredients to the wet ingredients, stirring until just combined.
Mix the remaining 1/4 cup sugar with the cinnamon in a small bowl.
Fill each cupcake liner with batter about halfway, sprinkle some cinnamon sugar, then cover with more batter until 3/4 full.
Bake for 20 minutes or until a toothpick inserted into the center comes out clean. Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
Beat room temperature butter and cream cheese until smooth. Gradually add powdered sugar and vanilla extract, beating until creamy.
Pipe or spread the frosting onto the cooled cupcakes.